CVE-2016-9820 in libav
Summary
by MITRE
libavcodec/mpegvideo_motion.c in libav 11.8 allows remote attackers to cause a denial of service (crash) via vectors involving left shift of a negative value.
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Analysis
by VulDB Data Team • 09/03/2020
The vulnerability identified as CVE-2016-9820 resides within the libavcodec component of the libav multimedia framework version 11.8, specifically in the mpegvideo_motion.c file. This issue represents a classic integer overflow condition that can be exploited remotely to trigger a denial of service scenario. The flaw manifests when the system processes certain multimedia content that involves motion compensation operations typical in video decoding. The vulnerability is categorized under CWE-191 as an integer underflow condition, where a negative value is subjected to a left shift operation, leading to undefined behavior and subsequent system instability.
The technical execution of this vulnerability involves the manipulation of video stream data that contains maliciously crafted motion vectors. During the decoding process, the MPEG video decoder attempts to perform bitwise left shift operations on negative integer values that result from improper boundary checks in motion vector calculations. When a negative value undergoes a left shift operation, the behavior becomes undefined according to the c programming language standard, causing the application to crash or behave unpredictably. This particular flaw demonstrates how seemingly benign multimedia processing can become a vector for system compromise when proper input validation and boundary checking mechanisms are absent.
From an operational perspective, this vulnerability presents a significant risk to systems that process untrusted video content, particularly those running libav-based applications such as video streaming services, media servers, or any system that handles multimedia file processing. The remote exploitation capability means that attackers can trigger the denial of service condition without requiring local access or authentication, making it particularly dangerous in networked environments. The impact extends beyond simple service disruption to potentially allow for more sophisticated attacks if combined with other vulnerabilities, as the crash can be leveraged to cause system instability or provide opportunities for further exploitation.
Security practitioners should implement immediate mitigations including updating to patched versions of libav where available, implementing input validation and sanitization for all multimedia content, and deploying network segmentation to limit exposure to potentially malicious content. The vulnerability aligns with ATT&CK technique T1203 - Exploitation for Client Execution, as it represents a remote code execution vector that can be exploited through multimedia content. Organizations should also consider implementing intrusion detection systems that can identify anomalous multimedia processing patterns and establish proper access controls to limit the impact of potential exploitation. The remediation strategy should include comprehensive testing of all multimedia processing pipelines and the implementation of robust error handling mechanisms that prevent undefined behavior from causing system crashes.